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JPA support for Querydsl
There is a newer version: 5.1.0
/*
 * Copyright 2015, The Querydsl Team (http://www.querydsl.com/team)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.querydsl.jpa;

import com.querydsl.core.Tuple;
import com.querydsl.core.types.CollectionExpression;
import com.querydsl.core.types.EntityPath;
import com.querydsl.core.types.Expression;
import com.querydsl.core.types.Ops;
import com.querydsl.core.types.dsl.ComparableExpression;
import com.querydsl.core.types.dsl.Expressions;
import com.querydsl.core.types.dsl.StringExpression;

/**
 * {@code JPAExpressions} provides factory methods for JPQL specific operations
 * elements.
 *
 * @author tiwe
 */
@SuppressWarnings("unchecked")
public final class JPAExpressions {

    /**
     * Create a new detached JPQLQuery instance with the given projection
     *
     * @param expr projection
     * @param 
     * @return select(expr)
     */
    public static  JPQLQuery select(Expression expr) {
        return new JPASubQuery().select(expr);
    }

    /**
     * Create a new detached JPQLQuery instance with the given projection
     *
     * @param exprs projection
     * @return select(exprs)
     */
    public static JPQLQuery select(Expression... exprs) {
        return new JPASubQuery().select(exprs);
    }

    /**
     * Create a new detached JPQLQuery instance with the given projection
     *
     * @param expr projection
     * @param 
     * @return select(distinct expr)
     */
    public static  JPQLQuery selectDistinct(Expression expr) {
        return new JPASubQuery().select(expr).distinct();
    }

    /**
     * Create a new detached JPQLQuery instance with the given projection
     *
     * @param exprs projection
     * @return select(distinct expr)
     */
    public static JPQLQuery selectDistinct(Expression... exprs) {
        return new JPASubQuery().select(exprs).distinct();
    }

    /**
     * Create a new detached JPQLQuery instacne with the projection zero
     *
     * @return select(0)
     */
    public static JPQLQuery selectZero() {
        return select(Expressions.ZERO);
    }

    /**
     * Create a new detached JPQLQuery instacne with the projection one
     *
     * @return select(1)
     */
    public static JPQLQuery selectOne() {
        return select(Expressions.ONE);
    }

    /**
     * Create a new detached JPQLQuery instance with the given projection
     *
     * @param expr projection and source
     * @param 
     * @return select(expr).from(expr)
     */
    public static  JPQLQuery selectFrom(EntityPath expr) {
        return select(expr).from(expr);
    }

    /**
     * Create a avg(col) expression
     *
     * @param col collection
     * @return avg(col)
     */
    public static > ComparableExpression avg(CollectionExpression col) {
        return Expressions.comparableOperation((Class) col.getParameter(0), Ops.QuantOps.AVG_IN_COL, (Expression) col);
    }

    /**
     * Create a max(col) expression
     *
     * @param left collection
     * @return max(col)
     */
    public static > ComparableExpression max(CollectionExpression left) {
        return Expressions.comparableOperation((Class) left.getParameter(0), Ops.QuantOps.MAX_IN_COL, (Expression) left);
    }

    /**
     * Create a min(col) expression
     *
     * @param left collection
     * @return min(col)
     */
    public static > ComparableExpression min(CollectionExpression left) {
        return Expressions.comparableOperation((Class) left.getParameter(0), Ops.QuantOps.MIN_IN_COL, (Expression) left);
    }

    /**
     * Create a type(path) expression
     *
     * @param path entity
     * @return type(path)
     */
    public static StringExpression type(EntityPath path) {
        return Expressions.stringOperation(JPQLOps.TYPE, path);
    }

    private JPAExpressions() {}

}